Lectrosonics Inc SMQE Manuale Utente

14

Microphone RF Bypassing

When used on a wireless transmitter, the microphone 

element is in the proximity of the RF coming from the 

transmitter. The nature of electret microphones makes 

them sensitive to RF, which can cause problems with 

the microphone/transmitter compatibility. If the electret 

microphone is not designed properly for use with wire-

less transmitters, it may be necessary to install a chip 

capacitor in the mic capsule or connector to block the 

RF from entering the electret capsule.
Some mics require RF protection to keep the radio 

signal from affecting the capsule, even though the 

transmitter input circuitry is already RF bypassed (see 

schematic diagram).
If the mic is wired as directed, and you are having dif-

ficulty with squealing, high noise, or poor frequency 

response, RF is likely to be the cause.
The best RF protection is accomplished by installing RF 

bypass capacitors at the mic capsule. If this is not pos-

sible, or if you are still having problems, capacitors can 

be installed on the mic pins inside the TA5F connector 

housing.

CAPSULE

CAPSULE

SHIELD

AUDIO

SHIELD

AUDIO

BIAS

Alternate locations for bypass capacitors

TA5F

CONNECTOR

TA5F

CONNECTOR

Preferred locations for bypass capacitors

Install the capacitors as follows:  Use 330 pF capaci-

tors. Capacitors are available from Lectrosonics. Please 

specify the part number for the desired lead style.

 

Leaded capacitors:  P/N 15117 

 

 

Leadless capacitors: P/N SCC330P

All Lectrosonics lavaliere mics are already bypassed 

and do not need any additional capacitors installed for 

proper operation.

Line Level Signals

The normal hookup for line level signals is:   Signal Hot 

to pin 5, Signal Gnd to pin 1 and pin 4 jumped to pin 1. 

This allows signal levels up to 3V RMS to be applied 

without limiting.
If more headroom is needed, insert a 20 k resistor in 

series with pin 5. Put this resistor inside the TA5F con-

nector to minimize noise pickup.